1. Field of the invention
The present invention concerns a machine intended for the welding of connections on solar cell electrodes and, more particularly, on silicon solar cells.
It is known that solar cells are built of a silicon wafer a first face of which is doped in a given conductivity type, then entirely covered with a silver coating to form one of the cell electrodes, and the second face of which is doped in the opposite type of conductivity, then covered by a silver coating in the form of a grid, the latter coating allowing for solar rays to penetrate down to the silicon wafer. It is this second face which is the sensitive face. A connection, usually a silver strip, is electrically welded to each electrode at a specific spot.
2. Description of the Prior Art
In accordance with prior state-of-the-art practice, welding of solar cell connections is achieved by applying the silver strip representing the connection which is placed at a given spot on the cell electrode with the cell being mounted between the abutting and parallel electrodes of an electric-pulsed welding machine. Such pulsed welding units are available on the market. They allow for the pressure adjustment which is required so that their electrodes press on the areas to be welded and also adjust for pertinent current and time of welding pulse.
It has occurred in the past that weldings implemented without properly preparing the cell electrode were of poor quality, mechanically - insofar as concerns their resistance to being pulled away from the connection -- as well as electricity -- insofar as concerns the preservation of the required cell electrical characteristics. Thus, still within the known state-of-the-art, the electrode part to weld which is to be subjected to the electrical welding operation of the cell electrode is either prepared chemically or mechanically to meet these requirements for mechanical and electrical quality. A known chemical preparation consists in cleaning the surface to be welded with potassium cyanide. Not only the use of this product is dangerous but results obtained are not entirely satisfactory. A known mechanical preparation involves smoothing out the surface to be welded with an eraser. This procedure gives rather satisfactory results but it is relatively long and delicate, particularly for the sensitive face electrode and it requires added cell cleaning before the welding procedure in order to eliminate residual eraser traces.